Raspberry Pi: Programming with ALSA

As covered in a previous article, Raspberry Pi can be used to capture and playback audio using a USB sound card. One can do the capture using ALSA utility aplay and arecord, or programmatically using the ALSA API. 

Example recording can be found in list 4 here: 
http://www.linuxjournal.com/article/6735?page=0,2

To accommodate for my setup, I had to: 

1. Change the hardware from "default" to "plughw:0,0" in snd_pcm_open(). 
2. I also replaced the write() with an fwrite() to output to a file. 

To install the relevant headers, I had to install the following package: 

sudo apt-get install libasound2-dev

Finally, to do the compile, don't forget to link to the ALSA library using the -l option: 
gcc record.c -lasound

The example code performs the capture at 44100Hz, signed 16 bit, 2 channels, and output to simple raw format without any file headers. To verify the recording, I had to specify all the parameters using aplay: 
aplay -f s16_le -r 44100 -c 2 test.out